As a player, he was a member of the 1972 United States Olympic Hockey team that surprisingly won the silver medal at the 1972 Winter Olympics. Ftorek also played for Team USA at the 1972 "Pool B" Ice Hockey World Championship where he was selected to the tournament all-star team. Originally drafted by the New England Whalers of the World Hockey Association in 1972, he instead signed with the NHL's Detroit Red Wings. However, the Red Wings regarded Ftorek as too small to make it as a professional and he only appeared in a handful of NHL games. Having spent most of his time in the minors with the AHL's Virginia Wings, Ftorek decided to move over to the WHA in 1974, and it was at this time the Whalers traded his WHA rights to the Phoenix Roadrunners. Ftorek quickly became the Roadrunners' biggest star and he made history in 1977 when he won the Gordie Howe Trophy as the league's most valuable player—the first American ice hockey player in major professional hockey to accomplish this feat. Ftorek confirmed his status as the most accomplished American player of the 1970s in the inaugural 1976 Canada Cup where he was elected MVP of Team USA and also was the US team's leading scorer. After playing parts of three seasons in Phoenix and when the Roadrunners franchise folded, Ftorek signed with the Cincinnati Stingers. After the WHA folded following the 1978–79 season, he signed with the Quebec Nordiques of the NHL and served as the team's captain in 1981. Ftorek played for Team USA at the 1981 Canada Cup tournament. He was traded to the New York Rangers during the 1981–82 NHL season, where he played through the 1984–85 NHL season and finished his NHL career. He played several seasons with the New Haven Nighthawks before retiring from professional play.

Ftorek completed his NHL career with 77 goals, 150 assists, 227 points, and 262 penalty minutes in 334 games. In his WHA career, Ftorek tallied 216 goals, 307 assists, 523 points, and 365 penalty minutes in 373 games, making him 6th on the WHA's all-time points list, and 9th in both the WHA's all-time career goal and assist leaders. His other WHA accomplishments include participating in the 1976, 1977, 1978 and 1979 WHA All-Star games as well as making the All-WHA 1st team in 1977, 1979 and the All-WHA 2nd team in 1976 and 1978.

He began his professional coaching career with the AHL's New Haven Nighthawks in 1985. He remained with then until the 1987–88 season when he moved up to the NHL as the Los Angeles Kings head coach until 1989. Following this, Ftorek was an assistant coach for the Quebec Nordiques and New Jersey Devils in the NHL. In 1992, he was named head coach of the AHL's Utica Devils and remained as head coach when the team became the Albany River Rats. In 1995, the same year the River Rats' parent club, the New Jersey Devils, won the Stanley Cup, Ftorek led the River Rats to the Calder Cup in the AHL. In 1996, Ftorek began his second stint as a New Jersey Devils assistant coach, then took the head coach's position in 1998. In 2000, he led the Devils back into the playoffs but was fired by Lamoriello with 9 games remaining in the regular season. Assistant coach Larry Robinson replaced him and the Devils went on to win their 2nd Stanley Cup. Ftorek remained with team as a scout, and had his name engraved on the Stanley Cup for second time in 2000. Ftorek joined the Boston Bruins as head coach in 2001. However, after two years of poor efforts by his teams, Ftorek was fired late in the 2002–03 season with only 9 games remaining in the season. Bruins GM Mike O'Connell took over as coach for the rest of the season. In 2003, Ftorek rejoined the Devils as head coach of their AHL affiliate in Albany. The team moved to Lowell, Massachusetts to become the Lowell Devils. Devs CEO/President/GM Lou Lamoriello stated that Ftorek would not be retained as head coach of the team.

In January 29, 2000, the Devils played a memorable game against Detroit. Particularly memorable for Ftorek was the game's officiating. Indeed, Ftorek was so irate over one call that he threw the team's wooden bench onto the ice surface. He was suspended for one game.

Ftorek holds the dubious distinction of being the only coach to be sacked by two different teams in the final days of what was a winning regular season for that team — first New Jersey in 1999–2000 and then Boston Bruins in 2002–03. His record was 41–20–8–5 with the Devils and 33–28–8–4 with the Bruins.